The co-pending application of Carl Schroder, Ser. No. 967,379, filed Dec. 7, 1978 and assigned to the assignee of this application, discloses a battery plate wrapping machine wherein successive battery plates are enclosed within a sheet of thermoplastic material and the over-lapped lateral edges of such sheet are sealed by acoustic guns. Opposite the discharge end of such guns, a roller anvil is positioned so as to hold the overlapped edges of the thermoplastic sheet in position for sealing and to also provide a reflection surface for directing the acoustic energy generated by the acoustic gun into the thermoplastic material. Such roller anvils were merely mounted for free rotation and were moved by the frictional engagement of the thermoplastic sheet with the anvil surfaces as the wrapped plate moved linearly past the heat energy source.
It has been my observation that the friction induced rotation of the anvils often effected an undesired displacement or wrinkling of the over-lapped edges of the thermoplastic sheets, thus resulting in an improper heat seal and a potentially defective wrap for the battery plate enclosed between the thermoplastic sheet. It was my further observation that this defective performance of existing heat sealing mechanisms employing roller anvils could be completely overcome if the roller anvil were rotated by a separate power source in exact synchronism with the linear movement of the thermoplastic sheet material contacted by the anvil so that there is no relative movement between such sheet material and the cylindrical surface of the roller anvil.